This invention relates to apparatus for in situ rejuvenation of asphalt pavement. More particularly this invention relates to a method and apparatus for controlling the mixing of milled aggregate and rejuvenating fluid in such rejuvenation.
Asphalt pavement consists essentially of an aggregate and sand mixture held together with a petroleum based binder, such as tar. With continued exposure to sun, moisture, traffic, freezing and thawing, asphalt surfaces degrade. The degradation is principally in the binder, rather than the aggregate and sand mixture which makes up the bulk of the asphalt. Also, much of the degradation occurs within the top two or three inches of the surface.
Traditionally, worn asphalt pavement was not restored but instead was torn up and replaced with new asphalt. This is a costly approach and creates a problem as to what to do with the torn up pavement. Accordingly, techniques and apparatus have been developed for restoring or rejuvenating the top few inches of an asphalt paved surface.
A typical road resurfacing apparatus has a heater for heating and softening the asphalt surface as it passes along the asphalt surface. Following the heater is a xe2x80x9crakexe2x80x9d or xe2x80x9cscarifierxe2x80x9d which breaks up or xe2x80x9cscarifiesxe2x80x9d the softened pavement. The scarified pavement is generally crushed or xe2x80x9cmilledxe2x80x9d, blended with rejuvenating fluid and optionally additional sand or aggregate and redeposited. The redeposited material is spread out and rolled to create a rejuvenated surface comparable in quality to the original surface before degradation.
In order to produce a rejuvenated surface of high quality, it is important to ensure that an appropriate amount of rejuvenation fluid is added. Generally, a core sample or several core samples are initially taken of the surface to be rejuvenated and a desired ratio of rejuvenation material to milled aggregate is analytically determined. Although the amount is relatively easy to determine, its control may prove difficult. Past asphalt rejuvenation machines have assumed a constant cutting or milling depth and a constant rate of machine travel in determining the rate of addition of rejuvenating fluid.
In practice, the machine speed may vary and as well, the depth of cut will generally vary because of surface irregularities and sloped surfaces. Accordingly, adding rejuvenation fluid at a rate based on constant speed and depth assumptions has produced rejuvenated surfaces with inconsistent properties.
It is an object of the present invention to provide a method and apparatus for more accurately controlling the mixing of asphalt aggregate with rejuvenating materials.
A method for controlling the mixing of asphalt aggregate with rejuvenating materials in an asphalt rejuvenating machine, said method comprising the steps of:
(i) dislodging a top layer of an asphalt paved surface;
(ii) passing a milling apparatus over the dislodged layer from step (i) to strip said top layer and break up the top layer of the asphalt paved surface to form a milled aggregate;
(iii) adding rejuvenating material to the milled aggregate;
(iv) transferring the milled aggregate to a mixer and blending the milled aggregate with said rejuvenating material to form a blended aggregate.
(v) discharging either the blended aggregate or the milled aggregate in a windrow of pre-determined width;
(vi) measuring the height of the windrow;
(vii) measuring a speed of travel of the asphalt rejuvenating machine;
(viii) comparing the height of the windrow with said speed and determining a volume rate of discharge from said mixer;
(ix) determining a desired rate of addition of the rejuvenating materials which corresponds to the volume rate of discharge and a pre-determined final composition; and,
(x) adjusting a rate of addition of the rejuvenating material in step (iii) to correspond to said desired rate of addition from step (ix).
An asphalt rejuvenating machine has a transport structure movable along an asphalt surface, a power plant mounted to the transport structure for providing motive force for the transport structure and a heater mounted to the transport structure for heating the asphalt surface. A rake mounted to the transport structure travels behind the heater for scarifying the asphalt surface to produce a scarified surface. A milling apparatus is mounted to the transport structure for milling the scarified surface to form a milled aggregate and to present the milled aggregate to a mixer. A rejuvenating fluid supply system is mounted to the transport structure for supplying rejuvenating fluid to the milled aggregate. The machine includes a mixer for blending the milled aggregate with the rejuvenating fluid and depositing a blended aggregate thus formed in a windrow of pre-determined width. The machine further includes a speed sensor for measuring the speed of travel of the transport structure and a height measuring device for measuring the height of the windrow. The machine further includes a comparator for comparing the speed of travel with the height to determine a volume rate of discharge of the blended aggregate. A controller associated with the rejuvenating fluid supply system is provided to vary a volume rate at which the rejuvenating fluid is added, based on the volume rate of discharge and the pre-determined final composition.
The rejuvenating fluid supply system may include a rejuvenating fluid tank, a sprayer for spraying the rejuvenating fluid on the milled aggregate, a pump fluidly communicating with the rejuvenating fluid tank and the sprayer for delivering the rejuvenating fluid from the tank to the sprayer, and a flow meter for determining a volume flow rate of the rejuvenating fluid.
The speed sensor may be mounted on an axle of the transport structure.
The mixer or the milling apparatus may have a discharge opening with a guide for determining the pre-determined width of the windrow, and a levelling device which rides along a top surface of the windrow.
The comparator may be part of a central processor unit which receives input from the speed sensor, the height measuring device, an operator control panel and the fluid flow meter. The central processor unit may also act as the controller by sending an output to the pump.